1. Field of the Invention
The present invention relates to a cutting tool made of surface-coated cemented carbide (hereinafter referred to as a surface-coated cemented carbide tool) provided with a hard coating layer that has excellent heat resistance, maintains high hardness and high strength at high temperatures and, as a consequence, exhibits excellent wear resistance even in high speed cutting operation of a high hardness steel, such as alloy tool steel or hardened bearing steel, which requires especially high heat resistance and generates much heat during the cutting operation.
Priority is claimed on Japanese Patent Application No. 2005-035684, filed Feb. 14, 2005, the content of which is incorporated therein by reference.
2. Description of Related Art
A surface-coated cemented carbide tool in general includes indexable insert that is removably attached at the tip of a cutting tool for machining of workpieces made of various steels or cast iron in turning or planning operation, drill bit or miniature drill bit that is used in drilling of workpieces and solid type end mill that is used for machining of workpieces in face milling, slot cutting (grooving) or stepping (shouldering) operation. The surface-coated cemented carbide tool also includes indexable end mill tool. The indexable insert of the indexable end mill tool is removably attached to an end mill and is used in cutting operation in a manner similar to that of the solid type end mill.
One known constitution of the surface-coated cemented carbide tool comprises a carbide substrate made of tungsten carbide-based cemented carbide (hereinafter abbreviated as WC) or titanium carbonitride-based cermet (hereinafter abbreviated as TiCN) of which surface is coated with a hard coating layer formed to a thickness of 0.1 to 20 μm by vapor deposition from a composite nitride of Ti, Al and Si (hereinafter referred to as (Ti, Al, Si)N) in single phase structure and composition of [Ti1−(X+Y)AlXSiY]N (X is in a range from 0.05 to 0.75 and Y is in a range from 0.01 to 0.10 in an atomic ratio). It is known that the (Ti, Al, Si)N layer has the hardness at high temperatures improved by the Al content, the strength at high temperatures improved by the Ti content and the heat resistance improved by the Si content.
It is also known that the surface-coated cemented carbide tool described above can be manufactured by coating the surface of the carbide substrate with the hard coating layer consisting of the (Ti, Al, Si)N layer in the following process: with the carbide substrate set in an arc ion plating apparatus, that is a variation of physical vapor deposition apparatus schematically illustrated in FIG. 3, arc discharge is generated by supplying a current of 90 A, for example, between an anode and a cathode (evaporation source) having of a Ti—Al—Si alloy of a predetermined composition within the apparatus where the ambient temperature is maintained at, for example, 500° C. by means of a heater, while nitrogen gas is introduced as a reaction gas into the apparatus so as to create a reaction atmosphere with a pressure of 2 Pa, and a bias voltage of −100 V, for example, is applied to the carbide substrate.    Patent Reference 1: Specification of Japanese Patent No. 2,793,773
There have been dramatic advancements in the performance of metal cutting machines in recent years. On the other hand, there are still strong demands for labor saving, energy saving and cost reduction in metal cutting operations, resulting in a trend toward higher cutting speed. The surface-coated cemented carbide tool of the prior art, provided that it is made of a material having a composition properly selected for the cutting conditions, performs satisfactorily in machining of steels and cast iron under ordinary cutting conditions. However, when used in high speed cutting operation of a high hardness steel, such as alloy tool steel or hardened bearing steel which has Rockwell hardness (C scale) as high as 50 or more and generates much heat during cutting operation, the surface-coated cemented carbide tool of the prior art wears off very quickly due to the insufficient heat resistance of the hard coating layer, thus failing in a relatively short period of time.
The present invention has been made in consideration of the problems of the prior art described above, and aims at providing a surface-coated cemented carbide tool that has excellent wear resistance and longer service life, and allows for labor saving, energy saving and cost reduction in metal cutting operations.